Compared to crude oil, biomass feedstocks have intrinsically high oxygen contents ranging from 6% for nature oil and fats to more than 50% for carbonhydrates. Conversion of these feedstocks to high value chemicals or “drop in” fuels without excessive sacrifice of carbon by decarboxylation/decarbonylation requires hydrodeoxygenation (HDO) as a mandatory process step. The HDO process is similar to the hydrotreating process which has been widely applied in petroleum refinery. It removes oxygen as “impurity” in the form of water by consumption of hydrogen.
Renewable diesels from HDO of plant oil and animal fats have been commercially produced by using conventional NiMo- and CoMo-based hydrotreating catalysts on zeolites or silica-alumina. The success can be attributed to the relatively low oxygen content, less impurities in the feedstocks, and importantly, the process design and optimization (U.S. Pat. No. 7,955,401, U.S. Publication No. 2010/0331586). These conventional hydrotreating catalysts were easily deactivated once be applied to hydrodeoxygenation of biomass-derived feedstocks. The fast deactivation might be due to the active oxygen functionalities, impurities, coke formation, water poisoning and the leaching of the silica-alumina based support. Moreover, the co-feed of sulfur compounds to maintain the activity of the conventional hydrotreating catalysts causes the contamination of downstream product (Chem. Rev., 110, 2010, 3552).
A process for preparing liquid fuels and chemical intermediates from biomass-derived hydrocarbons is described in U.S. Publication No. 2009/0255171. The method includes the steps of reacting in a single reactor an aqueous solution of sorbitol or glycerin in the present of a Pt—Re/C catalyst to yield a self-separating three-phase product stream comprising a vapor phase, an organic phase containing linear and/or cyclic mono-oxygenated hydrocarbons and an aqueous phase. In this process, the carbon exiting the reactor from sorbitol conversion consists primarily of alkanes, oxygenated compounds (C4-C6 alcohols, ketones, acids, and hetero-cylics), and COx (contributing to about 20-30% of total carbon in the product). Pt is regarded to be active for steam reforming and water-gas shift reaction and Re is regarded to be active for dehydration and C—O bonds cleavage. The process involves aqueous phase reforming reaction (APR). No additional hydrogen is required to co-feed with sugar alcohol. However, the carbon lost in the gas phase as CO2 is about 15% to 20%.
Due to the wide range of oxygen content and the nature of the biomass-derived feedstocks, for example: sugar and sugar alcohols, plant oil/animal fats, bio-crude from biomass pyrolysis or hydrothermal process, and lignin, the HDO process conditions vary a lot. In some cases, it requires operation under aqueous reaction condition, for example, the sugar and sugar alcohols HDO reaction. Therefore, water tolerance is a desired feature for the HDO catalysts to handle biomass-derived feedstocks.
Methods for preparing of polyacid-promoted zirconia extrudates which are hydrothermal stable in aqueous phase applications are described in U.S. publication No. 2011/0301021 which is hereby incorporated in its entirety. The zirconyl-promoter precursor is extruded in absence of any binder, extrusion aid or stabilizing agent. The calcined support comprises more than 85% tetragonal phase of zirconium oxide stabilized by polyacid promoter.